The objective of this research is to understand the intercellular and intracellular signaling mechanisms that trigger maturation of the mammalian oocyte. Fully grown oocytes in the ovary are surrounded by somatic cumulus and granulosa cells, which form the follicle. Oocytes are arrested in prophase I of meiosis. The preovulatory surge of luteinizing hormone (LH) causes the oocyte to resume meiosis, a process known as oocyte maturation. Oocyte maturation culminates in development of a mature egg that is released from the ovary during ovulation. The mechanism by which LH initiates the resumption of meiosis is not fully understood for any mammalian species. Cyclic adenosine monophosphate (cAMP) and calcium appear to have roles in initiating maturation; however, more definitive evidence for participation of calcium in triggering oocyte maturation is needed. Hormone dependent regulation of oocyte maturation will be studied in a system in which it is possible, for the first time, to examine the changes in intracellular free cAMP and calcium in the oocyte and surrounding follicular cells. Primordial and preantral follicles will be isolated from the ovaries of immature rats; when grow in culture, these form large follicles that closely mimic the organization and physiology of the normal follicle. This culture system permits optical imaging and cellular microinjection of oocytes in living follicles to learn how LH exerts its effects. Fluorescent probes for cAMP and calcium will be used to clarify the role of cAMP in oocyte maturation and to determine if calcium functions as a signaling agent in the process. Similar follicle culture systems are likely to be used in the future to culture human oocytes from primordial or preantral ovarian follicles. Before such culture systems are perfected, defining the metabolic and hormonal requirements for development of the granulosa cells and oocyte is important. The results from this research will provide a greater understanding of the signaling mechanisms that produce a mature egg from an immature oocyte.